Small extended-low-frequency-response loudspeaker enclosure



1956 E A. TAVARES 2,757,751

SMALL EXTENDEIjLOWFREQUENCYRESPON$E LOUDSPEAKER ENCLOSURE Filed April 7, 1952 5 J5 17 25' 9 a 17A g;

{9- INVENTOR. EQNEST- A. TAVAQE; BY Q. m.

AGENT United States Patent 7 SMALL EXTENDED-LOW-FREQUENCY-RESPONSE LOUDSPEAKER ENCLOSURE Generally speaking, the present invention relates to the sound reproduction art. More specifically, it relates to a novel, small loudspeaker enclosure arranged and so related to a loudspeaker as to greatly extend the low frequency range of useful acoustic radiation therefrom into a listening region.

It should be noted that this patent application is a continuation-inpart of my co-pending patent application entitled Novel, Small, Extended Low Frequency Response Loudspeaker Enclosure, Serial No. 163,994, filed May 24, 1950, subsequently granted July 19, 1955, as U. S. Patent No. 2,713,396 (which explicity and/ or implicitly discloses the inventive concepts, more specifically described, illustrated and claimed herein). The prior art problems and attempted (and only partially successful) solutions therefor, which caused applicant to invent the present invention are more fully set forth in the aforesaid U. S. patent. However, in the interest of brevity, it is thought unnecessary to recite them again herein.

Generally speaking, the present invention comprises a loudspeaker enclosure including a chamber carrying a loudspeaker diaphragm. Also provided is loading enclosure means in communication with a first side of said loudspeaker diaphragm whereby to effectively restrict air vibrations projected from said side of said loudspeaker diaphragm and to impart loading to said side of said loudspeaker diaphragm. Also included is first emission port means in effective communication with the other or second side of said loudspeaker diaphragm through said chamber. Said first emission port means being effectively provided with flow restricting means (usually slit means which can be of variable nature as defined by compliant auxiliary diaphragm means) arranged to restrict oscillatory flow of air through said emission port means, resulting from air vibrations projected from said second side of said loudspeaker diaphragm, in a manner such as to impart loading to said second side of said loudspeaker diaphragm.

In one preferred general form of the present invention, the flow restricting auxiliary diaphragm means maybe effectively positioned between the interior and the exterior of the chamber closely adjacent to the emission port means and may also effectively include low frequency acoustic radiator means adapted to radiate high level acoustic energy; and, in those forms of the present invention wherein front acoustic radiation is utilized, to be of a phase relationship such as to reinforce said front acoustic radiation.

In one general form of the present invention, the compliant auxiliary diaphragm means may comprise air pump means arranged to pump ambient air into the chamber when the loudspeaker diaphragm is vibrating in a selected low frequency range in a manner whereby the air pressure within the chamber will increase and in a manner whereby the compliance of the air within the chamber will be altered, which will thus effectively alter the variable slit emission means in a manner increasing 2,757,751 Patented Aug. 7, 1956 the effective moved air mass to effectively lower the resonant frequency.

In another general form of the present invention, the loading enclosure means may be effectively provided with second emission port means, which is further provided with second flow restricting means (usually slit means of a variable nature defined by second auxiliary diaphragm means) arranged to restrict oscillatory flow of air through said second emission port means, resulting from air vibrations projected from said first side of said loudspeaker diaphragm, in a manner such as to effectively impart loading to said side of said loudspeaker diaphragm while permitting the emission of sound from said second emission port means. Virtually all that has been said hereinabove in connection with the first auxiliary diaphragm means, is equally true of the just mentioned second diaphragm means. Therefore, no further description of the modifications of the auxiliary diaphragm means will be given at this time.

Also, in a preferred form of the present invention, high frequency by-pass means may be placed in effective communication with the first side of the loudspeaker diaphragm so as to effectively bypass the loading enclosure means (and the second emission port means).

It will be understood, from the above generic description of several basic forms of the present invention, that virtually all of the hereinabove mentioned disadvantages of prior art sound reproducing systems and/ or enclosures are virtually entirely eliminated and overcome in and through the use of the present invention.

For example, very little or no low frequency cancellation of front and back radiation occurs as a result of phase difference, as hereinbefore mentioned in connection with many prior art systems. The coupling, comprising the air mass in the enclosure and the compliant auxiliary diaphragm means, which acts as the effective acoustic output radiating surface (and variable emission slit modulating means) for the back radiation from the loudspeaker diaphragm and the effective alteration in the mass of the moved air, is such as to cause a very large output back radiation and front radiation to reinforce each other instead of cancelling out. And this in spite of the fact that the volume of air enclosed in the chamber may be very small and would ordinarily have a compliance such as to be incapable of producing the above mentioned resultsthe difference being produced by the compliantly mounted auxiliary diaphragm means, (effectively forming variable emission means) which greatly modifies the effective compliance of the small volume of air enclosed within the chamber and the effective mass of the moved air. All or at least part of what has been said in regard to the first auxiliary diaphragm means applies to the second diaphragm means (defining the second variable slit emission means) in effective communication with the first side of the loudspeaker diaphragm. Therefore, the explanation will not be repeated in connection with said second auxiliary diaphragm. However, it should also be noted that it tends to eliminate harmonics, over-tones and resonance of the speaker enclosure and/or loudspeaker.

Also, no substantial loss of power occurs, as in prior art infinite baffle systems, because of loss of the back acoustic radiation. In the preferred form of the present invention, the back acoustic radiation in the low frequency range reinforces the front acoustic radiation. Although, it should be noted, that in one form of the present invention wherein the loading enclosure means is closed, the back acoustic radiation (or vice versa) is the sole radiation output from the system.

- The loudspeaker enclosure of the present invention can be very small and have low frequency output characteristics as good as or better than a bass reflex cabinet a great deal larger. This is because the most critical facfor about a bass a reflex cabinet is the volume of the air enclosed therein which determines the coupling compliance, whereas, in the present invention, the coupling compliance is determined by the compliant means which may have any pre-determined value, or which can be adjusted to any desired value, thus eliminating cabinet volume as an important factor in the loudspeaker enclosure of the present invention. Furthermore, the loudspeaker enclosure of the present invention minimizes distortion and spurious harmonic generation in the low frequency range, and is capable of producing virtually pure fundamental tones as low as 30 cycles, or even lower in certain cases. This cannot be duplicated by any prior art system of anything like a comparable size. In addition, the present invention can do this with commercially available loudspeakers (even those with relatively small speaker cones).

With the above points in mind, it is an object of the present invention to provide a novel loudspeaker enclosure which can be made very small, and which, in combination with a loudspeaker, is capable of effectively radiating into a listening region substantial low frequency acoustic energy in a manner as good or better than very much larger prior art sound reproducing systems.

Another object of the present invention is to provide a novel loudspeaker enclosure provided with flow restricting means (usually variable slit compliant means) adapted to effectively alter the compliance of the air within the speaker enclosure and/or the effective mass of the air moved, whereby to cause the resonant frequency of the enclosure and/or a loudspeaker diaphragm associated therewith to be effectively lowered whereby to increase the low frequency output radiation.

It is a further object of the present invention to provide a system of the character set forth in either or both of the proceeding objects, which is provided with an additional speaker diaphragm loading enclosure which may or may not be provided with compliant variable slit emission means.

Other and allied objects will be apparent to those skilled in the art after a careful perusal, examination and study of the accompanying illustrations, the present specification and the appended claims.

To facilitate understanding, reference will be made to the hereinbelow described drawing, in which:

Fig. l is a view, partly in vertical section, of one illustrative embodiment of the present invention.

Fig. 2 is a vertical sectional view taken in the direction of the arrows IIII in Fig. 1.

Fig. 3 is a perspective view (greatly reduced in size) of another illustrative embodiment of the present invention.

Fig. 4 is a fragmentary view, partly in vertical section, similar in aspect to Fig. 1, but illustrates the slightly modified form of the present invention shown in Fig. 3.

Fig. 5 illustrates, in fragmentary vertical section, similar in aspect to Figs. 1 and 4, another slightly modified form of the invention.

Generally speaking, the present invention includes a chamber carrying a loudspeaker diaphragm and provided with loading enclosure means in communication with a first side of said loudspeaker diaphragm whereby to effectively restrict air vibrations projected from said first side of said loudspeaker diaphragm and whereby to impart loading to said first side of said loudspeaker diaphragm. First emission port means is also arranged in effective communication with the other or second side of said loudspeaker diaphragm through said chamber and is effectively provided with flow restricting means arranged to restrict oscillatory How of air through said emission port means, resulting from air vibrations projected from said second side of said loudspeaker diaphragm, in a man' ner such as to impart loading to said second side of said loudspeaker diaphragm.

In the specific form of the present invention illustrated in Figs. 1 and 2, the chamber is defined by a plurality of walls including a front wall 1, a back Wall 2, two side walls, 3 and 4 and a top and bottom wall, 5 and 6, joined together in spaced relationship to form a small chamber, indicated generally at '7. An additional loading enclosure, indicated generally at S, is defined by forward extensions 3A and 4A (not shown) and 5A and 6A of the side walls and the top and bottom walls 3, 4, 5 and 6, respectively, and an additional front wall 9. It will be noted that the loading enclosure 8 is in communication with the front side of the loudspeaker diaphragm 10 through a port 11 in the wall 1, across which the loudspeaker diaphragm 10 is effectively mounted by suitable mounting means.

The back wall 2 of the chamber 7 is provided with emission port means (in the specific example illustrated, centrally located and of circular shape) indicated at 12. In the specific example illustrated, the above referred to flow restricting means, comprises emission slit means, indicated generally at 13, defined by the positioning of an auxiliary diaphragm 14 which is illustrated as being circular and resiliently mounted by an inner mounting ring 17A fastened by fastening means 17B to the annulus 17; said mounting ring 17A being also fastened to spring means 15 spaced around the periphery thereof, the other ends of which are fastened to an outer mounting ring 16A, which is fastened with respect to the inside of the back wall 2 by fastening means, such as the screw means 16. Any other desired type of fastening means may be employed to resiliently mount the diaphragm means 14 with respect to the back wall 2 of the chamber 7. It should be noted that the auxiliary diaphragm 14 is mounted by the resilient means so that an annular outer portion 17 of the diaphragm 14 is positioned in virtually parallel, closely spaced relationship with respect to the inside of the back wall 2 immediately around the emission port 12 therethrough in such manner that the annular portion 17 of the diaphragm 14 lies closely adjacent to a corresponding annular portion of the back wall 2 of the box.

The arrangement is such that lateral vibratory oscillation of the diaphragm 14, which occurs as a result of back acoustic radiation from the loudspeaker diaphragm 10 in a selected low frequency range, tends to move the annular portion 17 of the diaphragm 14 toward and away from adjacent annular portion of the back wall 2, in a manner such that vibratory movement of the annular ring 17 tends to alter the variable air slit emission means 13 (and to thus alter the effective air mass moved), and to pump air into the chamber 7 through the slit means 13 between the rear surface of the annular ring 17 and the inside surface of the adjacent annular portion of the backwall '2, and such that vibratory oscillatory movement of the annular ring 17 toward the extreme right, as viewed in Fig. 1, tends to almost (or in some cases, completely) seal the port 12 and minimize (or prevent) the escape of air from within the enclosure 7 to ambient atmosphere. This tends to produce a pressure increase within the chamber 7 whenever the loudspeaker diaphragm 10 is vibrating in a selected low frequency range.

The pressure increase tends to effectively alter the variable slit emission means 13 thus effectively altering the mass of moved air in a manner tending to lower the resonant frequency of the chamber.

The air pressure increase (and/or density and/or compliance change) and/or the compliance of the resilient diaphragm and/or the spring coupling thereof to the back wall 2 of the chamber 7 is such as to alter the effective compliance against which the loudspeaker diaphragm 10 works in rearward oscillatory movement in a selected low frequency range. This effectively lowers the resonant frequency of the system and greatly increases the useful acoustic output in a selected low frequency low range.

In the specific example described and illustrated in Figs. 1 and 2, the diaphragm 14 is also provided with a central disc shaped portion 18, efiectively connected to the outer annular ring 17 by annular corrugations 19, which are intended to compliantly couple the outer annular ring 17 to the central disc portion 18.

In the specific example illustrated in Figs. 1 and 2, the central disc portion 18 is provided with suitable weight means 20, which may be fastened by any desired type of fastening means, such as is indicated at 21, to the disc 18, and which may be removable for replacement by a greater or lesser weight for modification of the low frequency response characteristics of the system. The central disc portion 18 and the outer annular ring 17 are connected by the flexible corrugations 19 for the purpose of reducing the resonant frequency of the diaphragm 14 and the weight carried thereby, since the effective low frequency limit which can be radiated into a listening region from the speaker enclosure is effectively limited by the resonant frequency of the auxiliary diaphragm (as well as the loudspeaker diaphragm).

Also, the central portion of the diaphragm 14 may act as a very efiicient acoustic radiator for radiating low frequency energy outwardly through the port 12, and the outer annular portion 17 of the diaphragm acts to effectively modulate air emitted through the emission slit means 13. It should be noted that either the annular ring 17 or the adjacent annular portion of the back wall 2 may be provided with suitable resilient means in order to prevent any spurious and extraneous noise from being produced, in the event that vibratory movement of the annular ring 17 toward the right causes it to actually make engagement with the adjacent annular portion of the back wall 2.

The spring means may be positionally adjustable so that the spacing between the annular ring 17 and the adjacent annular portion of the back wall 2 can be adjusted at will, so that, at maximum excursion of the annular ring 17, contact of the ring 17 and the wall 2 does not quite take place.

An another general form of the present invention, I contemplate arranging the spacing between the annular ring 17 and the adjacent annular portion of the back wall 2 so that outward movement of the ring 17 effectively closes the rear port 12 during the earlier portion of the outward stroke and thus produces a more effective air pumping action into the chamber 7. This form of the invention requires the use of resilient means positioned between the annular ring 17 and the rear wall 2, or requires that said wall 2 or the annular ring 17 be of resilient construction at the contacting surface.

It should be noted that the loading enclosure 8 acts to effectively load the front side of the loudspeaker diaphragm 10 and to thus greatly increase the elficiency of the entire system in the very low frequency range.

It should also be noted that the use of the terms front and back, as used in connection with the above description, are not to be taken in the limiting sense. Actually the ported wall 2 is the one emitting sound and would ordinarily be considered the front wall. However, for reasons of analogy with respect to the subsequent modifications of the invention to be described hereinafter, I have chosen to call the wall 2 the rear wall. It should also be understood that the direction of the loudspeaker diaphragm (and electro-magnetic actuating means therefor) can be reversed, if desired.

The modified form of the present invention shown in Figs. 3 and 4 is similar in all respects to the first form of the present invention illustrated in Figs. 1 and 2 except that the loading enclosure for the front side of the loudspeaker diaphragm is considerably different and includes a second variable slit emission port means and flow restricting means comprising a second auxiliary diaphragm. All of the similar parts will be indicated by the same reference numerals as employed in connection wtih Figs.

1 and 2 except that the reference numerals will be primed.

In this version of the invention, the loading enclosure comprises the space 22 immediately in front of the conical loudspeaker diaphragm 10 and extending through the port 11 to the front closure defined by the front diaphragm 23, which in the specific example illustrated, is of relatively stilf pie-pan-like construction provided with a central forwardly projecting portion 24 and an annular rim 25. The auxiliary diaphragm 23 is compliantly or resiliently mounted with respect to the loading enclosure 22 by suitable resilient means, indicated at 26, in a manner whereby at least a portion of the rim 25 (including the upper portion thereof as viewed in Fig. 4) can resiliently move toward and away from the adjacent portion of the front wall 1' whereby to define flow restricting variable emission slit means, indicated generally at 27.

The operation of the diaphragm 23 is in many (though not necessarily all) respects similar to the operation of other auxiliary diaphragms 14' (not shown, but identical to 14 in Figs. 1 and 2), the operation of which has been fully described hereinbefore in connection with the first form of the present invention.

Generally speaking, the front diaphragm 23 acts to eliminate undesirable distortion, harmonics, overtones, and resonance of the system. It also acts to effectively load the loudspeaker diaphragm 10' and effectively vary the air mass moved. It tends to produce a pure fundamental tone in the low frequency region and also allows the emission of certain of the high frequencies, although full high frequency reproduction is preferably to be obtained with a separate tweeter system or a combined tweeter system of the type disclosed in Fig. 5.

It should be noted that considerable control of the characteristics of the system can be exercised by adjusting the resiliency of the means 26 mounting the diaphragm 23, or by adjusting the volume of the enclosure 22, or by adjusting the size of the flow restricting emission means.

It should also be noted that the diaphragm 23 need not be resiliently mounted in the specific manner illustrated but can be mounted in any other desired manner, either symmetrically located with respect to the port 11 or otherwise. The mounting may, for example, be similar to that employed to mount the other auxiliary diaphragm 14' (not shown). Also, resilient cushioning means may be employed, if desired, for the purpose of minimizing chatter. Virtually any of the modifications of the other auxiliary diaphragm, hereinbefore mentioned, can be employed in connection with the front diaphragm 23. Furthermore, in certain modifications, the diaphragm may be positioned within the port means or may even be positioned on the inside of the front wall 1' (this will usually necessitate the repositioning of the loudspeaker diaphragm 10).

Fig. 5 illustrates another slightly modified version of the present invention including a high frequency by-pass means. Except for the by-pass means, and certain modifications 0f the loudspeaker and front auxiliary diaphragm occasioned thereby, this version of the present invention is similar to those hereinbefore described and illustrated. Therefore, similar parts will be indicated by similar reference numerals, doubly primed, however.

in this modification, the high frequency bypass means comprises a multiple, reticulated tweeter horn means, indicated generally at 28, extending concentrically through the conical loudspeaker diaphragm 10 and outwardly through the port 11", and effectively through the diaphragm, indicated generally at 23". The effective penetration of the diaphragm 23" by the tweeter horn 28 is accomplished by providing the outer portion of the tweeter horn 28 with a circular member having a circular forwardly projecting edge 29 resiliently connected by annular corrugations 30 to an outer annular ring portion 31 of the diaphragm 23". It will be understood that high frequency sound is emitted through the tweeter horn 23, which is fixed, and that low frequency sound is radiated from the loudspeaker diaphragm l0 and is emitted through the flow restricting emission slit means 27", defined by the resiliently movable outer annular ring 31, which acts in the same general manner as the diaphragm 23 previously described in the second form of the present invention and illustrated in Figs. 3 and 4.

Numerous modifications and variations of the present invention will occur to those skilled in the art after a careful study hereof. All such properly within the spirit and scope of the present invention are intended to be included and comprehended herein as fully as if specifically described, illustrated and claimed herein.

For example, the shape and configuration of the loudspeaker enclosure is not limited to the form illustrated herein, but may assume a great variety of forms, and may be of integral or non-integral construction, and may be made of any desired materials.

Either or both of the diaphragm means and/ or emission port means and/or flow restricting means need not be positioned in any particular wall or walls of the system, but can be positioned in great variety of different relationships.

The structure, arrangement, and composition of either or both of the diaphragm means, and/ or the emission port means and/or the slit means and/ or the flow restricting means can be modified substantially from that illustrated herein. In fact the flow restricting means can be separated from the emission port means, if desired.

Either or both of the diaphragm means need not be positioned on a certain specified side of a wall but may be located in any selected position with respect thereto. Either or both of the diaphragm means may be compliantly coupled with respect to the enclosure or may be inherently compliant or may be relatively stiff and provided with compliant coupling means so as to have pistonlike action. Either or both of the diaphragrns may have several relatively stiff portions connected by flexible portions therebetween, if desired, or they may be provided with weight means (which may be adjustable, if desired) in order to alter the effective resonant frequencies thereof. Either or both may be arranged so as to not effectively close the associated port but to merely oscillate or vibrate in spaced relationship with respect thereto. if desired, either or both of the diaphragms may be arranged to have two (or more) portions connected by relatively flexible portions in a manner such that the resonant frequency of one of said portions is different from the resonant frequency of the other of said portions, to facilitate the operation of the system. in certain cases, the compliant diaphragm means may not be positioned between the interior of the enclosure and ambient atmosphere but may be positioned within the enclosure in a manner whereby to produce the hereinbefore mentioned advantageous operational features.

It should be noted that either or both of the auxiliary diaphragrns may be positionally transposed, if desired. In other Words, a diaphragm of the type indicated herein at 14 may be positioned for cooperation with the front port 11 (either inside or outside of the wall 1), and a diaphragm of the type indicated at 23 can be positioned for cooperation with respect to the rear port l2; (either inside or outside of the rear wall 2) or, if desired, both front and back diaphragms may be of the same type simi lar either to the front diaphragm 23 or the back diaphragm l4 (and generic forms thereof). This latter basic form of the invention is more specifically described, illustrated and claimed in my co-pending patent application, Serial No. 298,107 filed July 10, 1952.

The embodiments of the present invention specifically described, illustrated and claimed herein are exemplary only, and are not intended to limit the scope of the present invention, which is to be interpreted in the light of the prior art and the appended claims only, with due consideration for the doctrine of equivalents.

I claim:

1. A loudspeaker enclosure including a chamber carrying a loudspeaker diaphragm, comprising: loading enclosure means effectively in communication with the one side of said loudspeaker diaphragm and cooperable therewith to effectively restrict air vibrations projected from one side of said loudspeaker diaphragm and to impart loading to said side of said loudspeaker diaphragm; emission port means in effective communication with the other side of said loudspeaker diaphragm through said chamber; said emission port means being effectively provided with flow restricting means cooperable therewith to restrict oscillatory flow of air through said emission port means resulting from air vibrations projected from said other side of said loudspeaker diaphragm in a manner such as to impart loading to said side of said loudspeaker diaphragm, said flow restricting means comprising compliant peripheral slit defining means.

2. A system of the character defined in claim 1, including high frequency by-pass horn means in effective communication with the first mentioned side of the loudspeaker diaphragm and effectively by-passing the loading enclosure means.

3. A loudspeaker enclosure including a chamber carrying a loudspeaker diaphragm, comprising: loading enclosure chamber means efiectively in communication with one side of said loudspeaker diaphragm and cooperable therewith to effectively restrict air vibrations projected from one side of said loudspeaker diaphragm and to impart loading to said side of said loudspeaker diaphragm; emission port means in effective communication with the other side of said loudspeaker diaphragm through said chamber; said emission port means being provided with compliant flow restricting means in effective communication with the interior f said chamber and cooperable With said emission port means to restrict oscillatory flow of air through said emission port means resulting from air vibrations projected from said other side of said loudspeaker diaphragm in a manner such as to impart loading to said other side of said loudspeaker diaphragm; said compliant flow restricting means comprising an auxiliary thin-sheet diaphragm means resiliently mounted in closely spaced position across the emission port means.

4. A system of the character defined in claim 3, wherein the flow restricting compliant auxiliary diaphragm means is so spaced with respect to the emission port means as to define resiliently variable emission slit means.

5. A. system of the character defined in claim 4,. wherein the auxiliary diaphragm means has a substantially greater surface area than the area of the emission port means immediately adjacent thereto whereby vibratory movement of. the auxiliary diaphragm means toward and away from the emission port means, in response to low frequency vibration of the loudspeaker diaphragm, will tend to pump air into the chamber and increase the mean air pressure therein, thus altering the effective compliance of the air within the chamber and altering the variable slit emission means in a manner increasing the effective air mass moved.

6. A system of the character defined in claim 5, including weight means carried by the auxiliary diaphragm means for causing said diaphragm means to have the proper low resonant frequency.

7. A system of the character defined in claim 6, wherein the auxiliary diaphragm means includes a central disc shaped portion and an outer annulus resiliently joined together.

8. A system of the character defined in claim 7, where in the outer annulus is resiliently mounted with respect to the interior of the emission port means and wherein the central disc-shaped portion of the auxiliary diaphragm means carries the weight means for lowering the resonant frequency.

9. A system of the character defined in claim 8, including high frequency by-pass horn means in efiective communication with the first mentioned side of the loudspeaker diaphragm and effectively by-passing the loading enclosure means.

10. A loudspeaker enclosure including a chamber carrying a loudspeaker diaphragm, comprising: loading enclosure means in effective communication with a first side of said loudspeaker diaphragm and cooperable therewith to effectively restrict air vibrations projected from said side of said loudspeaker diaphragm and to impart loading to said side of said loudspeaker diaphragm; first emission port means in effective communication with a second side of said loudspeaker diaphragm through said chamber; said first emission port means being effectively provided with a first flow restricting means in effective communication with the interior of said chamber and cooperable wth said first emission port means to restrict oscillatory fiow of air through said emission port means resulting from air vibrations projected from said second side of said loudspeaker diaphragm in a manner such as to impart loading to said side of said loudspeaker diaphragm; and second emission port means in effective communication wtih the first side of said loudspeaker diaphragm through the loading enclosure means, said second emission port means being effectively provided with a second compliant flow restricting means in effective communication with the interior of the loading enclosure and cooperable with said second emission port means to restrict oscillatory flow of air through said second emission port means resulting from air vibrations projected from said first side of said loudspeaker diaphragm in a manner such as to effectively impart loading to said first side of said loudspeaker diaphragm; said first flow restricting means comprising a first auxiliary thinsheet diaphragm resiliently mounted in closely spaced position across the first emission port means.

11. A system of the character defined in claim 10, wherein the second compliant flow restricting means comprises a second auxiliary thin-sheet diaphragm resiliently mounted in closely spaced position across the second emission port means.

12. A system of the character defined in the claim 11, wherein the second flow restricting compliant auxiliary diaphragm means is so spaced with respect to the second emission port means as to define resiliently variable emission slit means.

13. A system of the character defined in claim 12, including high frequency by-pass horn means in effective communication with the first mentioned side of the loudspeaker diaphragm and effectively by-passing the loading enclosure means.

14. A loudspeaker enclosure including a chamber carrying a loudspeaker diaphragm, comprising: loading enclosure means in effective communication with a first side of said loudspeaker diaphragm and cooperable therewith to effectively restrict air vibrations projected from said side of said loudspeaker diaphragm and to impart loading to said side of said loudspeaker diaphragm; first emission port means in effective communication with a second side of said loudspeaker diaphragm through said chamber; said emission port means being effectively provided with fiow restricting means cooperable therewith to restrict oscillatory How of air through said emission port means resulting from air vibrations projected from said second side of said loudspeaker diaphragm in a manner such as to impart loading to said side of said loudspeaker diaphragm; and second emission port means in effective communication with the first side of said loudspeaker diaphragm through the loading enclosure means; said second emission port means being effectively provided with second flow restricting means cooperable therewith to restrict oscillatory flow of air through said second emission port means resulting from air vibrations projected from said first side of said loudspeaker diaphragm in a manner such as to effectively impart loading to said first side of said loudspeaker diaphragm; both of the flow restricting means including slit means; said first flow restricting means comprising a first auxiliary thin-sheet diaphragm means resiliently mounted in closely spaced position across the first emission port means; said second flow restricting means comprising a second auxiliary thin-sheet diaphragm means resiliently mounted in closely spaced position across the second emission port means.

15. A system of the character defined in claim 14, wherein the first flow restricting auxiliary diaphragm means is so spaced with respect to the first emission port means as to define a resiliently variable first emission slit means, and wherein the second flow restricting auxiliary diaphragm means is so spaced with respect to the second emission port means as to define resiliently variable second emission slit means.

16. A system of the character defined in claim 15, wherein the first auxiliary diaphragm means has a substantially greater surface area than the area of the first emission port means immediately adjacent thereto whereby vibratory movement of the first auxiliary diaphragm means toward and away from the first emission port means in response to low frequency vibration of the loudspeaker diaphragm will tend to pump air into the chamber and increase the mean air pressure thereof thus altering the effective compliance and density of the air within the chamber and altering the variable slit emission means in a manner increasing the effective air mass moved.

17. A system of the character defined in claim 16, including weight means carried by the auxiliary diaphragm means for causing said diaphragm means to have the proper low resonant frequency.

References Cited in the file of this patent UNITED STATES PATENTS 1,787,946 La Rue Jan. 6, 1931 1,866,921 Black July 12, 1932 1,878,162 Mead Sept. 20, 1932 1,988,250 Olson Jan. 15, 1935 2,359,348 Barclay Oct. 3, 1944 2,496,589 Marquis Feb. 7, 1950 FOREIGN PATENTS 51,523 Denmark Apr. 14, 1936 116,565 Australia Feb. 25, 1943 663,734 Great Britain Dec. 27, 1951 

